The number of available anti-fungal agents is now increasing, as is the incidence of significant yeast infections. The National Committee for Clinical Laboratory Standards has recently developed a proposed standard for yeast susceptibility testing. While there appears to be increasing clinical interest in the results of in vitro test results to help guide clinical decision-making in selecting agents to treat yeast infections, it remains to be determined how well in vitro results correlate with clinical responsiveness. In this study, we intend 1) to compare commercially- available testing procedures such as the E-test and a colorimetric method (Alamar Biosciences, Inc.) with results obtained by the proposed reference method, 2) to attempt to determine the clinical relevance of in vitro susceptibility results by correlating in vitro and clinical results in so far as possible, and 3) to collect clinical yeast isolates and assess any changes with time of susceptibility results.